This invention relates to an electrode wire for an electrical discharge machining apparatus, and especially to an electrode wire for an electrical discharge machining apparatus having a covering layer.
As a conventional electrode wire for an electrical discharge machining apparatus, a Cuxe2x80x94Zn alloy wire (a brass wire) containing Zn of 32 to 36 weight percent is used.
Besides this, a composite wire composed of a core metallic wire formed of a steel wire and a covering layer formed of Cuxe2x80x9435Zn alloy is known as an electrode wire for an electrical discharge machining apparatus with height strength. Moreover, an electrode wire for the same, which is composed of a core metallic wire formed of Cu alloy, such as Cuxe2x80x940.15Sn or Cuxe2x80x940.15Ag alloy, and a covering layer formed of Cuxe2x80x9435Zn alloy is known (Japanese Patent Publication No. 6-47130).
As a method for increasing electrical discharge machining speed and obtaining an electrode wire for the same with high efficiency, a method, in which concentration of Zn of Cuxe2x80x94Zn alloy is increased or heat-resisting property of the electrode wire is improved by adding Al to Cuxe2x80x94Zn alloy, is known (Furukawa Electric Review, No.75, March, 1985).
Recently, further elevation of electrical discharge machining speed is demanded from a view point of improvement of productivity. In order to meet the aforementioned demand, an electrode wire with covering layer for an electrical discharge machining apparatus, which is composed of a core metallic wire formed of Cuxe2x80x942.0Sn, Cuxe2x80x940.3Sn, Cuxe2x80x9413Zn, Cuxe2x80x940.6Ag or Cuxe2x80x944.0Znxe2x80x940.3Sn and a covering layer formed of a Cuxe2x80x94Zn alloy containing Zn of high weight percent, is proposed (Japanese Patent Kokai No.5-339664).
However, in the aforementioned electrode wire for the electrical discharge machining apparatus, since the Cuxe2x80x94Zn alloy layer contains Zn of 38 to 49 weight percent, the Cuxe2x80x94Zn alloy layer is formed of a mixing composition of xcex1 and xcex2 phases, or a single phase composition of only xcex2 phase. Since cold working of the Cuxe2x80x94Zn alloy layer becomes difficult as a composition of xcex2 phase becomes dominant, the aforementioned electrode wire for the electrical discharge machining apparatus can be produced only by hot working (hot extrusion), hence production cost thereof becomes high.
Moreover, in the aforementioned electrode wire for the electrical discharge machining apparatus, since Cu alloy, such as Cuxe2x80x942.0Sn, Cuxe2x80x940.3Sn, Cuxe2x80x9413Zn, Cuxe2x80x940.6Ag or Cuxe2x80x944.0Znxe2x80x940.3Sn, is adopted as material of the core metallic wire, following disadvantages are inevitable. This product is detective in workability in the process of drawing in case that the core metallic wire is formed of Cuxe2x80x942.0Sn. Heat-resisting property (strength at high temperature) of the product is low, and at the time of practical use, instability of discharge occurs because of the breaking of a wire or the elongation of the wire before the breaking in case that the core metallic wire is formed of Cuxe2x80x9413Zn. In the product with low electrical conductivity (in case that the core metallic wire is formed of Cuxe2x80x944.0Znxe2x80x940.35Sn) or low heat-resisting property, improvement of electrical discharge machining speed is not satisfactory. In case of alloy containing Ag, material cost becomes high. Referring to the core metallic wire, since heat-resisting property of a Cu alloy disclosed in Japanese Patent Kokai No. 6-47130 is insufficient, electrical discharge machining speed cannot be improved (Cuxe2x80x940.15Sn), and material cost of Cu alloy containing Ag is high in general.
Accordingly, it is an object of the invention to solve the aforementioned problems and provide an electrode wire for an electrical discharge machining apparatus composed of a core metallic wire formed of Cu alloy and a covering layer formed of Cuxe2x80x94Zn alloy, which is low priced in material cost, has sufficiently high electrical conductivity and heat-resisting property and is suited for improving electrical discharge machining speed.
It is a further object of the invention to provide an electrode wire for an electrical discharge machining apparatus, which is composed of a core metallic wire formed of Cu alloy and a Cuxe2x80x94Zn alloy covering layer formed of a single phase composition of only xcex1 phase.
It is a still further object of the invention to provide an electrode wire for an electrical discharge machining apparatus, which is composed of a core metallic wire formed of Cu alloy and a Cuxe2x80x94Zn alloy covering layer formed of a mixing phase composition of xcex1 and xcex2 phases.
According to the first feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
a core metallic wire formed of Cuxe2x80x940.02 to 0.2Zr alloy or Cuxe2x80x940.15 to 0.25Snxe2x80x940.15 to 0.25In in alloy, and
a covering layer formed of Cuxe2x80x94Zn alloy.
According to the second feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
a core metallic wire formed of Cuxe2x80x940.02 to 0.2 Zr alloy or Cuxe2x80x940.15 to 0.25Snxe2x80x940.15 to 0.25 In alloy, and
a Cuxe2x80x94Zn alloy covering layer formed of a single phase composition of only xcex1 phase.
According to the third feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
a core metallic wire formed of Cuxe2x80x940.02 to 0.2Zr alloy or Cuxe2x80x940.15 to 0.25Snxe2x80x940.15 to 0.25 In alloy, and
a Cuxe2x80x94Zn alloy covering layer formed of a mixing composition of xcex10 and xcex2 phases.
The invention pays the attention to material of a core metallic wire of an electrode wire for an electrical discharge machining apparatus having a covering layer formed of Cuxe2x80x94Zn alloy.
The reason for limiting material of the core metallic wire to Cu-alloy is that tensile strength and electrical conductivity at high temperature is satisfactory. A steel wire is omitted, because it is defective in straightness, when it comes loose. Moreover, it is difficult to apply the steel wire to a processing machine. A Cu wire is omitted because tensile strength thereof at high temperature is insufficient.
The reason for selecting the aforementioned numerical values on composition of the core metallic wire will be explained.
In Cuxe2x80x940.02 to 0.2Zr alloy, when concentration of Zr is less than 0.02 weight percent, heat-resisting property of alloy is insufficient and instability of discharge arises, and when concentration of Zr is more than 0.2 weight percent, it exceeds the limit of solid solution of Cuxe2x80x94Zn alloy and precipitation of Cu3Zr starts, and the breaking of a wire is apt to occur, so that concentration of Zr is limited within a range of 0.02 to 0.2 weight percent. Since Cuxe2x80x940.05 to 0.16Zr alloy, in which concentration of Zr is 0.05 to 0.16 weight percent, is widely used for various purposes as Cuxe2x80x940.16Zr alloy, this alloy is the most economical in Cuxe2x80x94Zr alloy.
Next, concentrations of Sn and In in Cuxe2x80x940.15 to 0.25Snxe2x80x940.15 to 0.25 In alloy will be discussed. Sn and In are added to alloy in order to increase the strength of alloy, but the effect of Sn on a decrease of the electrical conductivity of alloy is more noticeable than that of In. Since the electrical conductivity of the wire should be kept to be high from a view point of stability of discharge characteristic, it is desirable that concentration of In is higher that of Sn. However, since In is high-priced, concentration of In is kept to be less than 0.25%. Accordingly, there is necessity to increase the amount of addition of Sn, but the conductivity of alloy noticeably decreases in case that concentration of Sn is more than 0.25 weight percent. The aforementioned composition is selected on the basis of trade-off between improvement of discharge characteristic and economical consideration.
Moreover, concentration of Zn of Cuxe2x80x94Zn alloy will be discussed. In case that concentration of Zn is 32 to 38 weight percent, Cuxe2x80x94Zn alloy can be formed of a single phase composition of a phase, and in the region of xcex1 phase, although tensile strength and hardness increases as concentration of Zn increases, hardness is not so high and Cuxe2x80x94Zn alloy can be processed by cold working. Accordingly, manufacturing process including drawing is easily carried out. Concentration of Zn of 32 to 36 weight percent corresponds to that of Cuxe2x80x9435Zn alloy (65/35 brass), which is widely used for various purposes. Cuxe2x80x9435Zn alloy is formed of a single phase composition of xcex1 phase, suited for cold working, easily obtained on the market and favorable from a viewpoint of economy.
Furthermore, since the thickness of the covering layer formed of Cuxe2x80x94Zn alloy is consumed by about 30 xcexcm in an electrical discharge machining process of high efficiency, the thickness of the covering layer formed of Cuxe2x80x94Zn alloy is selected to be more than 30 xcexcm in order to avoid a situation that the breaking of a wire occurs, and less than 40 xcexcm, because the electrical conductivity of the wire becomes insufficient for fulfilling the function of an electrode wire for an electrical discharge machining apparatus in case that the thickness of the covering layer is more than 40 xcexcm.